The invention relates to a preferably once recordable optical data storage medium containing a triazacyanine dye as the light-absorbing compound in the information layer, and to a process for its production.
Recordable optical data storage media using special light-absorbing substances or mixtures thereof are particularly suitable for use in high-density recordable optical data storage media which operate with blue laser diodes, and in particular GaN or SHG laser diodes (360-460 nm), and/or for use in DVD-R or CD-R discs, which operate with red (635-660 nm) or infrared (780-830 nm) laser diodes, and the application of the abovementioned dyes to a polymer substrate, in particular polycarbonate, by spin-coating or vapour deposition.
There has recently been an enormous growth in the sales of recordable compact discs (CD-R, 780 nm), which represent the technically established system.
The next generation of optical data storage mediaxe2x80x94DVDsxe2x80x94is currently being introduced onto the market. By using shorter-wave laser radiation (635 to 660 nm) and a higher numerical aperture NA, the storage density can be increased. The recordable format is in this case the DVD-R.
Today, optical data storage formats which use blue laser diodes (based on GaN, JP 08191171 or Second Harmonic Generation SHG JP 09050629) (360 nm to 460 nm) with a high laser power, are being developed. Recordable optical data storage media will therefore also be used in this generation. The achievable storage density depends on the focussing of the laser spot in the information plane. The spot size is proportional to the laser wavelength xcex/NA. NA is the numerical aperture of the objective lens used. The aim is to use the smallest possible wavelength xcex for obtaining the highest possible storage density. Based on semiconductor laser diodes, 390 nm are presently possible.
The patent literature describes dye-based recordable optical data storage media which are equally suitable both for CD-R and DVD-R systems (JP-A 11 043 481 and JP-A 10 181 206). In order to obtain high reflectivity, a high modulation level of the readout signal and sufficient sensitivity during recording, use is made of the fact that the IR wavelength 780 nm of the CD-R is located at the base of the long-wavelength slope of the absorption peak of the dye and the red wavelength 635 nm or 650 nm of the DVD-R is located at the base of the short-wavelength slope of the absorption peak of the dye. In JP-A 02 557 335, JP-A 10 058 828, JP-A 06 336 086, JP-A 02 865 955, WO-A 09 917 284 and U.S. Pat. No. 5,266,699 this concept is extended to cover the working wavelength range of 450 nm on the short-wavelength slope and the red and IR range on the long-wavelength slope of the absorption peak.
In addition to the abovementioned optical properties, the recordable information layer consisting of light-absorbing organic substances must have a morphology which is as amorphous as possible, in order to keep the noise signal during recording or reading as small as possible. For this purpose it is particularly preferable, when applying the substances by spin-coating from a solution or by vapour deposition and/or sublimation, to prevent crystallization of the light-absorbing substances during the subsequent top-coating with metallic or dielectric layers in vacuo.
The amorphous layer of light-absorbing substances should preferably have high thermal stability, since otherwise additional layers of organic or inorganic material applied by sputtering or vapour deposition onto the light-absorbing information layer form blurred boundaries due to diffusion and thus have an adverse effect on the reflectivity. In addition, if a light-absorbing substance has inadequate thermal stability at the boundary to a polymeric substrate, it can diffuse into the latter and again have an adverse effect on the reflectivity.
If the light-absorbing substance has too high a vapour pressure, it can sublime during the abovementioned sputtering or vapour deposition of additional layers in a high vacuum and thus reduce the desired layer thickness. This in turn has a negative effect on reflectivity.
The object of the invention is therefore to provide suitable compounds which meet the high demands (such as light stability, a favourable signal-to-noise ratio, damage-free application to the substrate material, etc.) for use in the information layer of a recordable optical data storage medium, in particular for high-density recordable optical data storage formats in a laser wavelength range of 340 to 680 nm.
Surprisingly, it has been found that light-absorbing compounds from the triazacyanine group of dyes are particularly suitable for satisfying the abovementioned requirement profile.
The invention therefore relates to an optical data storage medium containing a preferably transparent substrate which has optionally already been coated with one or more reflecting layers and onto the surface of which a photorecordable information layer, optionally one or more reflecting layers and optionally a protective layer or an additional substrate or a top layer are applied, which data storage medium can be recorded on and read using blue or red light, preferably laser light, wherein the information layer contains a light-absorbing compound and optionally a binder, characterized in that at least one triazacyanine dye is used as the light-absorbing compound.
The light-absorbing compound should preferably be thermally modifiable. Preferably the thermal modification is carried out at a temperature of  less than 600xc2x0 C., particularly preferably at a temperature of  less than 400xc2x0 C., very particularly preferably at a temperature of  less than 300xc2x0 C., and in particular at a temperature of  less than 200xc2x0 C. Such a modification can for example be the decomposition or chemical modification of the chromophoric centre of the light-absorbing compound.
A triazacyanine of the formula I is preferred 
in which
X1 and X3 represent nitrogen or
X1xe2x80x94R1 and X3xe2x80x94R2 independently of one another represent S,
X2 and X4 independently of one another represent O, S, CH or Nxe2x80x94R3,
R1, R2 and R3 independently of one another represent C1- to C16-alkyl, C3- to C6-alkenyl, C5- to C7-cycloalkyl or C7- to C16-aralkyl,
the rings A and B, each together with X1, X2 and X3, X4, respectively, and the C atom in each case bound therebetween, independently of one another represent a five- or six-membered aromatic or quasiaromatic heterocyclic ring, which can contain 1 to 4 hetero atoms and/or can be benzo- or naphtho-fused and/or substituted by non-ionic radicals, and
Anxe2x88x92 represents an anion.
Suitable non-ionic radicals are for example C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro, C1- to C4-alkoxycarbonyl, C1- to C4-alkylthio, C1- to C4-alkanoylamino, benzoylamino and mono- or di-C1- to C4-alkylamino.
Alkyl, alkoxy, aryl and heterocyclic radicals can optionally contain additional radicals such as alkyl, halogen, nitro, cyano, COxe2x80x94NH2, alkoxy, trialkylsilyl, trialkylsiloxy or phenyl, the alkyl and alkoxy radicals can be straight-chain or branched, the alkyl radicals can be partially halogenated or perhalogenated, the alkyl and alkoxy radicals can be ethoxylated or propoxylated or silylated, adjacent alkyl and/or alkoxy radicals on aryl or heterocyclic radicals can together form a three- or four-membered bridge and the heterocyclic radicals can be benzo-fused and/or quaternized.
Particulary preferably the ring A of the formula 
represents benzothiazol-2-yl, benzoxazol-2-yl, benzimidazol-2-yl, thiazol-2-yl, isothiazol-3-yl, imidazol-2-yl, pyrazol-5-yl, 1,3,4-thiadiazol-2-yl, 1,2,4-thiadiazol-5-yl, 1,2,3-thiadiazol-5-yl, 1,3,4-triazol-2-yl, 2- or 4-pyridyl or 2- or 4-quinolyl, wherein the aforementioned rings can optionally be substituted by C1- to C6-alkyl, C1- to C6-alkoxy, fluorine, chlorine, bromine, iodine, cyano, nitro, C1- to C6-alkoxy-carbonyl, C1- to C6-alkylthio, C1- to C6-acylamino, C6- to C10-aryl, C6- to C10-aryloxy, C6- to C10-arylcarbonylamino, mono- or di-C1- to C6-alkylamino, Nxe2x80x94C1- to C6-alkyl-Nxe2x80x94C6- to C10-arylamino, pyrrolidino, morpholino or piperazino, and
the ring B of the formula 
represents benzothiazol-2-ylidene, benzoxazol-2-ylidene, benzimidazol-2-ylidene, thiazol-2-ylidene, isothiazol-3-ylidene, imidazol-2-ylidene, pyrazol-5-ylidene, 1,3,4-thiadiazol-2-ylidene, 1,2,4-thiadiazol-5-ylidene, 1,2,3-thiadiazol-5-ylidene, 1,3,4-triazol-2-ylidene, pyridin-2- or 4-ylidene, quinolin-2- or 4-ylidene, wherein the aforementioned rings can in each case be substituted by C1- to C6-alkyl, C1- to C6-alkoxy, fluorine, chlorine, bromine, iodine, cyano, nitro, C1- to C6-alkoxycarbonyl, 5 C1- to C6-alkylthio, C1- to C6-acylamino, C6- to C10-aryl, C6- to C10-aryloxy, C6- to C10-arylcarbonylamino, mono- or di-C1- to C6-alkylamino, Nxe2x80x94C1- to C6-alkyl-Nxe2x80x94C6- to C10-arylamino, pyrrolidino, morpholino or piperazino.
In a particularly preferred form the triazacyanines are those of the formula 
wherein
R1 and R2 independently of one another represent C1- to C16-alkyl, C3- to C6-alkenyl, C5- to C7-cycloalkyl or C7- to C16-aralkyl,
X5 represents N or Cxe2x80x94R6,
X6 represents N or Cxe2x80x94R7,
R4 to R7 independently of one another represent hydrogen, C1- to C4-alkyl, C1- to C4-alkoxy, C1- to C4-alkylthio, cyano, C1- to C4-alkoxycarbonyl, nitro, mono- or bis-C1- to C4-alkylamino, Nxe2x80x94C1- to C4-alkyl-Nxe2x80x94C7- to C15-aralkylamino, Nxe2x80x94C1- to C4-alkyl-Nxe2x80x94C5- to C17-cycloalkylamino, Nxe2x80x94C1- to C4-alkyl-Nxe2x80x94C6- to C10-arylamino, C6- to C10-arylamino, pyrrolidino, piperidino, piperazino or morpholino or
R4;R6 and R5;R7 independently of one another form a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge which can be substituted by methyl, chlorine, methoxy or cyano and
An31  represents an anion.
Suitable anions Anxe2x88x92 are all monovalent anions or one equivalent of a polyvalent anion. Preferably the anions are colourless. Suitable anions are for example chloride, bromide, iodide, tetrafluoroborate, perchlorate, hexafluorosilicate, hexafluorophosphate, methosulphate, ethosulphat, C1- to C10-alkanesulphonate, C1- to C10-perfluoroalkane sulphonate, C1- to C10-alkanoate optionally substituted by chlorine, hydroxyl or C1- to C4 alkoxy, benzene sulphonate, naphthalene sulphonate or biphenyl sulphonate optionally substituted by nitro, cyano, hydroxyl, C1- to C25-alkyl, perfluoro-C1- to C4-alkyl, C1- to C4-alkoxycarbonyl or chlorine, benzene disulphonate, naphthalene disulphonate or biphenyl disulphonate optionally substituted by nitro, cyano, hydroxyl, C1- to C4-alkyl, C1- to C4-alkoxy, C1- to C4-alkoxycarbonyl or chlorine, benzoate optionally substituted by nitro, cyano, C1- to C4-alkyl, C1- to C4-alkoxy, C1- to C4-alkoxycarbonyl, benzoyl, chlorobenzoyl or toluoyl, the anion of naphthalenedicarboxylic acid, diphenyl ether disulphonate, tetraphenyl borate, cyanotriphenyl borate, tetra-C1- to C20-alkoxyborate, tetraphenoxyborate, 7,8- or 7,9-dicarba-nido-undecaborate(1-) or (2-), which are optionally substituted on the B- and/or C-atoms by one or two C1- to C12-alkyl or phenyl groups, dodecahydro-dicarbadodecaborate(2-) or Bxe2x80x94C1- to C12-alkyl-C-phenyl-dodecahydro-dicarbadodecaborate(1-).
Bromide, iodide, tetrafluoroborate, perchlorate, methane sulphonate, benzene sulphonate, toluene sulphonate, dodecylbenzene sulphonate and tetradecane sulphonate are preferred.
In a very particularly preferred form the triazacyanines used are those of the formula (IV),
wherein
R1 and R2 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
X5 represents N or Cxe2x80x94R6,
X6 represents N or Cxe2x80x94R7,
R4 and R5 independently of one another represent hydrogen, methyl, ethyl, methoxy, cyano, methoxycarbonyl, dimethylamino, diethylamino, dipropylamino, dibutylamino, N-methyl-N-cyanoethylamino, N-methyl-N-methoxyethylamino, N-methyl-N-hydroxyethylamino, bis-(cyanoethyl)amino, bis-(methoxyethyl)amino, bis-(hydroxyethyl)-amino, N-methyl-N-benzylamino, N-methyl-N-phenylamino, phenyl-amino, methoxyphenylamino, pyrrolidino, piperidino, N-methyl-, N-ethyl-, N-hydroxyethyl- or N-cyanoethylpiperazino or morpholino,
R6 and R7 independently of one another represent hydrogen, methyl, ethyl, methoxy or cyano or
R4;R6 and R5;R7 independently of another form a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge, which can be substituted by methyl, chlorine, methoxy or cyano, and
Anxe2x88x92 represents an anion.
In a form which is also eminently preferred the triazacyanines used are those of the formula (IV),
wherein
R1 and R2 are identical and represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxy-ethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
X5 represents Cxe2x80x94R6,
X6 represents Cxe2x80x94R7,
R4;R6 and R5;R7 are identical and form a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge, which can be substituted by methyl, chlorine, methoxy or cyano, and
Anxe2x88x92 represents an anion.
In a form which is also eminently preferred the triazacyanines used are those of the formula (IV),
wherein
R1 and R2 are identical and represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxy-ethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
X5 represents N,
X6 represents N,
R4 and R5 are identical and represent dimethylamino, diethylamino, dipropylamino, dibutylamino, N-methyl-N-cyanoethylamino, N-methyl-N-methoxyethylamino, N-methyl-N-hydroxyethylamino, bis-(cyanoethyl)amino, bis-(methoxyethyl)amino, bis-(hydroxyethyl)-amino, N-methyl-N-benzylamino, N-methyl-N-phenylamino, phenyl-amino, methoxyphenylamino, pyrrolidino, piperidino, N-methyl-, N-ethyl-, N-hydroxyethyl- or N-cyanoethylpiperazino or morpholino, and
Anxe2x88x92 represents an anion.
In a form which is also eminently preferred the triazacyanines used are those of the formula (IV),
wherein
R1 and R2 are identical and represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxy-ethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
X5 represents N,
X6 represents Cxe2x80x94R7,
R4 represents dimethylamino, diethylamino, dipropylamino, dibutylamino, N-methyl-N-cyanoethylamino, N-methyl-N-methoxy-ethylamino, N-methyl-N-hydroxyethylamino, bis-(cyanoethyl)amino, bis-(methoxyethyl)amino, bis-(hydroxyethyl)amino, N-methyl-N-benzylamino, N-methyl-N-phenylamino, phenylamino, methoxy-phenylamino, pyrrolidino, piperidino, N-methyl-, N-ethyl-, N-hydroxyethyl- or N-cyanoethylpiperazino or morpholino,
R5;R7 forms a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94bridge, which can be substituted by methyl, chlorine, methoxy or cyano, and
Anxe2x88x92 represents an anion.
For a recordable optical data storage medium according to the invention which is recorded on and read using light from a blue laser, such triazacyanine dyes are preferred whose absorption maximum xcexmax2 is in the range from 420 to 550 nm, wherein the wavelength xcexxc2xd at which the extinction on the short-wavelength slope of the absorption maximum of the wavelength xcexmax2 is half the extinction value at xcexmax2, and the wavelength xcex{fraction (1/10)}, at which the extinction on the short-wavelength slope of the absorption maximum of the wavelength xcexmax2 is a tenth of the extinction value at xcexmax2, are preferably in each case no further than 50 nm away from each other. Preferably such a triazacyanine dye does not display a shorter-wave maximum xcexmax1 at a wavelength below 350 nm, particularly preferably below 320 nm, and very particularly preferably below 290 nm.
Preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 410 to 530 nm.
Particularly preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 420 to 510 nm.
Very particularly preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 430 to 500 nm.
In these triazacyanine dyes xcexxc2xd and xcex{fraction (1/10)}, as defined above, are preferably no further than 40 nm, particularly preferably no further than 30 nm, and very particularly preferably no further than 20 nm away from each other.
For a recordable optical data storage medium according to the invention which is recorded on and read using light from a red laser, such triazacyanine dyes are preferred whose absorption maximum xcexmax2 is in the range from 500 to 650 nm, wherein the wavelength xcexxc2xd at which the extinction on the long-wavelength slope of the absorption maximum of the wavelength xcexmax2 is half the extinction value at xcexmax2 and the wavelength xcex{fraction (1/10)}, at which the extinction on the long-wavelength slope of the absorption maximum of the wavelength xcexmax2 is a tenth of the extinction value at xcexmax2, are preferably in each case no further than 50 nm away from each other. Preferably such a triazacyanine dye does not display a longer-wave maximum xcexmax3 at a wavelength below 750 nm, particularly preferably below 800 nm, and very particularly preferably below 850 nm.
Preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 530 to 630 nm.
Particularly preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 550 to 620 nm.
Very particularly preferred triazacyanine dyes are those with an absorption maximum xcexmax2 of 580 to 610 nm.
In these triazacyanine dyes xcexxc2xd and xcex{fraction (1/10)}, as defined above, are preferably no further than 40 nm, particularly preferably no further than 30 nm, and very particularly preferably no further than 20 nm away from each other.
At the absorption maximum xcexmax2 the triazacyanine dyes have a molar extinction coefficient xcex5 of  greater than 20000 l/mol cm, preferably  greater than 30000 l/mol cm, particularly preferably  greater than 40000 l/mol cm and very particularly preferably  greater than 60000 l/mol cm.
The absorption spectra are, for example, measured in solution.
Triazacyanines of the formula (I) are known, for example, from EP-A 0 567 846.
The light-absorbing substances described guarantee sufficiently high reflectivity ( greater than 10%) of the optical data storage medium in the unrecorded state and sufficiently high absorption for the thermal degradation of the information layer upon spotwise illumination with focussed light, if the wavelength of the light is in the range from 360 to 460 nm and 600 to 680 nm. The contrast between the recorded and unrecorded areas of the data storage medium is effected by the change in reflectivity in terms of the amplitude as well as the phase of the incident light as a result of the changed optical properties of the information layer following thermal degradation.
The triazacyanine dyes according to the invention especially guarantee a particularly high change in the refractive index upon the transition from the unrecorded to the recorded state.
The triazacyanine dyes are preferably applied to the optical data storage medium by spin-coating. The triazacyanines can be mixed with other triazacyanines or with other dyes having similar spectral properties. The information layer can contain additives in addition to the triazacyanine dyes, such as binders, wetting agents, stabilizers, diluents and sensitizers as well as other constituents.
In addition to the information layer, the optical data storage medium can contain other layers such as metal layers, dielectric layers and protective layers. Metals and dielectric layers are used, for example, for adjusting the reflectivity and the thermal balance. Depending on the laser wavelength, the metals can be gold, silver or aluminium, etc. Dielectric layers are, for example, silicon dioxide and silicon nitride. Protective layers are, for example, photocurable surface coatings, (pressure-sensitive) adhesive layers and protective films.
Preferred pressure-sensitive adhesive layers mainly consist of acrylic adhesives. Nitto Denko DA-8320 or DA-8310, which are disclosed in the patent JP-A 11-273147, can for example be used for this purpose.
The optical data storage medium has, for example, the following layer assembly (cf. FIG. 1): a transparent substrate (1), optionally a protective layer (2), an information layer (3), optionally a protective layer (4), optionally an adhesive layer (5) and a top layer (6).
Preferably, the optical data storage medium assembly can contain:
a preferably transparent substrate (1), onto whose surface at least one photorecordable information layer (3), which can be recorded on using light, preferably laser light, optionally a protective layer (4), optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface a protective layer (2), at least one information layer (3) which can be recorded on using light, preferably laser light, optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface optionally a protective layer (2), at least one information layer (3) which can be recorded on using light, preferably laser light, optionally a protective layer (4), optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface at least one information layer (3) which can be recorded on using light, preferably laser light, optionally an adhesive layer (5) and a transparent top layer (6) are applied.
Alternatively the optical data storage medium has for example the following layer assembly (cf. FIG. 2): a preferably transparent substrate (11), an information layer (12), optionally a reflecting layer (13), optionally an adhesive layer (14) and an additional, preferably transparent, substrate (15).
The invention also relates to optical data storage media according to the invention which are recorded on using blue or red light, and in particular laser light.
The following examples illustrate the subject matter of the invention: